1. Field of the Invention
The present invention relates generally to fluid vaporizing devices such as aerosol generators.
2. Brief Description of the Related Art
Aerosols are useful in a wide variety of applications. For example, it is often desirable to treat respiratory ailments with, or deliver drugs by means of, aerosol sprays of finely divided particles of liquid and/or solid, e.g., powder, medicaments, etc., which are inhaled into a patient""s lungs. Aerosols are also used for purposes such as providing desired scents to rooms, distributing insecticides and delivering paint and lubricant.
Various techniques are known for generating aerosols. For example, U.S. Pat. Nos. 4,811,731 and 4,627,432 disclose devices for administering medicaments to patients in which a capsule is pierced by a pin to release a medicament in powder form. A user then inhales the released medicament through an opening in the device. While such devices may be acceptable for use in delivering medicaments in powder form, they are not suited to delivering medicaments in liquid form. The devices are also, of course, not well-suited to delivery of medicaments to persons who might have difficulty in generating a sufficient flow of air through the device to properly inhale the medicaments, such as asthma sufferers. The devices are also not suited for delivery of materials in applications other than medicament delivery.
Another well-known technique for generating an aerosol involves the use of a manually operated pump which draws liquid from a reservoir and forces it through a small nozzle opening to form a fine spray. A disadvantage of such aerosol generators, at least in medicament delivery applications, is the difficulty of properly synchronizing inhalation with pumping. More importantly, however, because such aerosol generators tend to produce particles of large size, their use as inhalers is compromised because large particles tend to not penetrate deeply into the lungs.
One of the more popular techniques for generating an aerosol including liquid or powder particles involves the use of a compressed propellant, often containing a chloro-fluoro-carbon (CFC) or methylchloroform, to entrain a material, usually by the Venturi principle. For example, inhalers containing compressed propellants such as compressed gas for entraining a medicament are often operated by depressing a button to release a short charge of the compressed propellant. The propellant entrains the medicament as the propellant flows over a reservoir of the medicament so that the propellant and the medicament can be inhaled by the user.
In propellant-based arrangements, however, a medicament may not be properly delivered to the patient""s lungs when it is necessary for the user to time the depression of an actuator such as a button with inhalation. Moreover, aerosols generated by propellant-based arrangements may have particles that are too large to ensure efficient and consistent deep lung penetration. Although propellant-based aerosol generators have wide application for uses such as antiperspirant and deodorant sprays and spray paint, their use is often limited because of the well-known adverse environmental effects of CFC""s and methylchloroform, which are among the most popular propellants used in aerosol generators of this type.
In drug delivery applications, it is typically desirable to provide an aerosol having average mass median particle diameters of less than 2 microns to facilitate deep lung penetration. Propellant based aerosol generators are incapable of generating aerosols having average mass median particle diameters less than 2 microns. It is also desirable, in certain drug delivery applications, to deliver medicaments at high flow rates, e.g., above 1 milligram per second. Some aerosol generators suited for drug delivery are incapable of delivering such high flow rates in the 0.2 to 2.0 micron size range.
Commonly owned U.S. Pat. Nos. 5,743,251 and 6,234,167, which are hereby incorporated by reference in their entirety, disclose aerosol generators, along with certain principles of operation and materials used in an aerosol generator, as well as methods of producing an aerosol, and an aerosol.
The invention provides a dual capillary fluid vaporizing device that includes a fluid source, a power source, and a heater arrangement electrically heated by the power source. The heater arrangement includes first and second capillary tubes, with the capillary tubes having inlet ends in fluid communication with the fluid source and the heater arrangement being operable to vaporize fluid in the capillary tubes. A first electrode supplies electrical current to the first capillary tube such that electrical current passes along at least a portion of the first capillary tube. An electrical connection connects the capillary tubes such that the electrical current supplied to the first capillary tube passes along at least a portion of the second capillary tube, and a second electrode is electrically connected to the second capillary tube such that the capillary tubes are electrically connected in series to the power source.
The invention also provides a method of vaporizing fluid that includes supplying fluid from the fluid source to first and second capillary tubes, and heating the first and second capillary tubes by passing electrical current from the power source along the first capillary tube, through the electrical connection interconnecting the first and second capillary tubes, and along the second capillary tube, the electrical current being effective to heat the capillary tubes such that the fluid therein is volatilized and exits the capillary tubes as a vapor.